In November, Germany's highest appeals court in Karlsruhe found the 32-year-old guilty of abetting the murder of 246 passengers and crew who died on four aircraft used in the attacks of September 11, 2001.

The decision overturned a ruling in 2005 which had convicted Motassadeq of belonging to a "terrorist organisation" and handed him a seven-year jail sentence, but cleared him of abetting mass murder.

That court said he was a lower-tier member of the group led by Mohammed Atta, the leader of the suicide attacks, and Motassadeq's lawyers say he knew nothing about the plot to fly aeroplanes into targets in New York and Washington.

Court appeal

But prosecutors successfully argued in November that under a "division of labour" within Atta's group, Motassadeq played a key role in running the financial affairs of other cell members and covering up their absences from Germany before the attacks.

Zacarias Moussaoui, a French citizen of Moroccan descent who received a life sentence from a US court last May, is the only other person convicted of having any ties to the attacks.